Field of the Invention
The present invention relates to the manufacture of ammonium salts used, in particular, as fertilizers.
In particular, processes for manufacturing ammonium salts using a tubular reactor are disclosed by numerous documents (patents U.S. Pat. No. 2,568,901, U.S. Pat. No. 2,755,176, U.S. Pat. No. 2,902,342). According to these processes, the two reactants (acid and base) are introduced into a tubular reaction chamber in substantially stoichiometric proportions, that is to say mole for mole. The reaction chamber proper is extended by a tube of diameter substantially similar to that of the chamber, in which the neutralization reaction continues. Of the supply conduits of the two reactants, one may deliver axially into the reaction chamber and the other tangentially. Their mixing is promoted by the presence of elements which can generate turbulence, for example venturis, baffles, etc.
The total length of the reaction chamber and of the tube which extends it is in general large (often more than 50 times the diameter of the tube), so as to allow a neutralization reaction which is as complete as possible.
It has been found that, in this type of reactor and process, the high temperature resulting from the exothermic reaction between the base and the acid (in the case of ammonia and nitric acid, this temperature may be between 150 and 220.degree. C.) makes the unneutralized nitric acid droplets extremely corrosive. This results in rapid destruction of the entire reactor, making it necessary to replace it after a period which may be of the order of 6 to 12 months. Longer service could be achieved by using, for example, titanium instead of stainless steel, but this would make the cost of the reactor prohibitive.
It is also found in these known processes that, in spite of the stoichiometric proportions used and the overall length of the reactor, the reaction is not complete and ammonia remains in the vapour which is separated from the nitrate solution at the outlet of the reactor.
The invention forming the subject of this patent proposes mainly to solve the first of the two problems mentioned above, namely to reduce or, if possible, eliminate the corrosion of the reactor.
It also proposes to reduce the ammonia losses and consequently improve the yield of the neutralization.